Brett Watson's white Ford Mondeo, seen in Minto on the day of his alleged murder. Photo: NSW Police

But police have revealed they believe a fourth person was also involved in the alleged bashing murder of the St Marys man.

They are also trying to track the movements of Mr Watson's car, a 1999-model white Ford Mondeo with registration plates BAX47A, that was seen in the Minto area on October 20, the day of his alleged murder.

Brett Watson's body was found in Greengrove on October 21. Photo: NSW Police

A motorcyclist discovered Mr Watson's body in secluded bush near the intersection of Mangrove Creek Road and Wisemans Ferry Road in Greengrove, a few kilometres from a yoga retreat, about 7.30am on October 21.

Police will allege in court that Mr Watson was killed at a unit on Morris Street in St Marys, before his body was dumped in Greengrove.